Control of Y2O3 phase and its nanostructure formation through a very high energy mechanical milling

The formation behavior of Y2O3 ceramic particles was studied by employing a very high energy ball milling (milling energy: ∼165 kJ/g·hit, milling speed: 1000 rpm). Both the XRD and HRTEM studies revealed that the high impact strain energy generated during the milling caused a drastic phase transition from the original C-type cubic (space group Ia3, a=10.58 Å) to the metastable B-type monoclinic (space group C2/m, a=13.89 Å), finally followed by a partial solid-state amorphization. The cubic phase was difficult to be reduced down to smaller than 10 nm, while the monoclinic phase was stabilized at sizes smaller than 10 nm with a mean crystallite size of 7.57 nm. Consequently, the existence of Y2O3 at a nanoscale smaller than 10 nm is possible by forming metastable monoclinic crystals, which are strain-induced.

The fig shows the solid-state phase formation of Y2O3 by very high energy input into the particles during milling: ordered body-centered cubic phase (space group Ia3, a=10.58 Å) nanocrystalline monoclinic phase (space group C2/m, a=13.89 Å) disordered monoclinic phase partial amorphous phase. The formation of Y2O3 smaller than 10 nm was strongly dependent on whether the phase transition from cubic to monoclinic occurred.Figure optionsDownload as PowerPoint slideHighlights
► This paper analyses very high energy milling behavior of coarse Y2O3 particles.
► A drastic phase transition from cubic to monoclinic occurred with a partial amorphization.
► An existence of Y2O3 smaller than 10 nm is possible by forming strain-induced monoclinic crystals.